In general, mobile communication systems have been developed to provide communication services while guaranteeing user mobility. Thanks to rapid technological advancement, mobile communication systems are capable of providing not only voice communication services but also high-speed data communication services.
Recently, the 3rd Generation Partnership Project (3GPP) has been working to standardize specifications for the Long Term Evolution (LTE) system as a next generation mobile communication system. The LTE system aims to realize high-speed packet based communication supporting a data rate of several hundreds Mbps exceeding existing data rates, and standardization thereof is near completion.
Active efforts are underway to develop the LTE-Advanced (LTE-A) system by introducing various new communication schemes to the LTE system. Carrier aggregation (CA) is a representative one of newly introduced communication schemes. Unlike an existing user equipment that uses one downlink carrier and one uplink carrier for data transmission and reception, a user equipment supporting carrier aggregation uses multiple downlink carriers and multiple uplink carriers.
In current LTE-A, only intra-ENB carrier aggregation is specified. This reduces potential applicability of carrier aggregation and hampers aggregation of macro and pico cells particularly in a situation where multiple pico-cells and one macro-cell are deployed in an overlapping manner.
To cope with the increasing demand for wireless data traffic after commercialization of 4G communication systems, active efforts are underway to develop enhanced 5G or pre-5G communication systems. As such, 5G or pre-5G communication systems are referred to as beyond 4G communication systems or post LTE systems. To achieve high data rates, use of the extremely high frequency (mmWave) band (e.g. 60 GHz band) is expected in a 5G communication system. To reduce propagation pathloss and to increase propagation distance at the mmWave band, use of various technologies such as beamforming, massive MIMO, full dimensional MIMO (FD-MIMO), array antenna analog beamforming and large scale antenna are under discussion for 5G communication systems. To enhance system networks, various technologies such as advanced small cell, cloud radio access network (cloud RAN), ultra-dense network, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, Coordinated Multi-Points (CoMP) and interference cancellation are under development for 5G communication systems. In addition, for 5G communication systems, hybrid FSK and QAM modulation (FQAM) and sliding window superposition coding (SWSC) are under development for advanced coding modulation (ACM), and filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA) and sparse code multiple access (SCMA) are under development for advanced access.
Meanwhile, the Internet is evolving from a human centered network where humans create and consume information into the Internet of Things (IoT) where distributed elements or things process and exchange information. Big data processing through cloud servers and IoT technology are being combined into the Internet of Everything. To realize IoT services, base technologies such as sensing, wired/wireless communication and network infrastructure, service interfacing and security are needed, and technologies interconnecting things such as sensor networks, Machine-to-Machine (M2M) or Machine Type Communication (MTC) are under development. In IoT environments, it is possible to provide intelligent Internet technology services, which collect and analyze data created by interconnected things to add new values to human life. Through convergence and combination with existing information technology, IoT technology is applied to various areas such as smart homes, smart buildings, smart cities, smart or connected cars, smart grids, health-care, smart consumer electronics, and advanced medical instruments.
Accordingly, various attempts are being made to apply 5G communication systems to IoT networks. For example, sensor networks and machine-to-machine or machine type communication are being realized by use of 5G communication technologies including beamforming, MIMO and array antennas. Application of big data processing to cloud RANs is an instance of convergence of 5G communication technology and IoT technology.